This project is directed toward further characterization of bulbospinal pathways that are excitatory or inhibitory to sympathetic preganglionic neurons in the spinal cord of cats. Electrophysiological techniques are combined with anatomical, neurochemical and neuropharmacological approaches to determine the functional nature of bulbospinal pathways that appear, from histochemical studies, to contain the monoaminergic transmitters, norepinephrine and serotonin. Considerable evidence indicates that these monoamines regulate the excitability of the spinal neurons that control sympathetic activity including blood pressure. Studies also include determination of the effects of drugs that alter blood pressure on the relevant bulbospinal pathways. Since a number of studies by other investigators indicate that these pathways may be involved in experimental hypertension, further determination of their basic properties and their susceptibility to selected drugs may contribute to better understanding of the etiology and treatment of essential hypertension.